Apparatus for processing acoustic damping material



Fil ed June 1. 1954 NOV. 24., 1959 R BLACK 2,913,838

APPARATUS FOR PROCESSING ACOUSTIC DAMPING MATERIAL 2 Sheets-Sheet l Q m ,1 'I'TOR N15) Nov. 24, 1959 R. D. BLACK APPARATUS FOR PROCESSING ACOUSTIC DAMPING MATERIAL Filed June 1. 1954 2 Sheets-Sheet 2 INVENTOR a A W l1 TTORNE Y w A mu mu as 7/////////////// \R AN NT I. MN Y 9 k N.\1 m\ H w mm IR ////Z V///////////A A.

United States Patent APPARATUS FOR PROCESSING ACOUSTIC DAMPING MATERIAL Application June 1, 1954, Serial No. 433,636

Claims. or. 38-44) This invention relates to an apparatus for processing acoustic damping materials, and, and particularly, to a mechanism for obtaining damping material with a uniform prescribed acoustic impedance.

One of the problems involved in controlling the, response of acoustic transducers is that of obtaining a damping material with a given acoustic impedance. The high frequency response, particularly of the smaller transducers such as microphones and earphones, is often greatly afiected by the damping material used in the front cavity. For example, in many cases transducers have been designed to meet certain requirements and it has been found that the high frequency limits had to be controlled with a damping material having specific acoustic properties. In the experimental stages of such a transducer various damping materials are used until the one giving the desired amount of control is found.

The problem becomes more difficult due to the fact the although one piece of material may give the desired results, a second sample from the same piece of material, taken some distance from the first sample, may give undesirable results while a third sample may react differently from the first two. This is due to the fact that normal weaving processes do not produce a material having uniform acoustic properties.

An object of this invention, therefore, is to provide a mechanism for processing a woven material so that it has uniform acoustic damping properties.

Another object of this invention is to provide a mechanism for simultaneously processing a material to achieve certain acoustic properties and measuring theacoustic properties of the material. j

A further object of this invention is to provide a mechanism for processing a woven damping material to maintain the acoustic impedance of the material within certain predetermined parameters.

In accordance with the present invention, a mechanism for accomplishing these objects comprises afcalender, means for keeping a substantially constant tension on a strip of material entering the calender, a device for measuring the acoustic impedance of the strip as it passes through the device, and means for keeping a substantially constant tension on the strip as it passes said measuring device. The acoustic impedance of a woven material may be controlled by the application of heat, by the speed of calendering or by the pressure applied in the calendering process. One or more of these variables may be controlled to keep the acoustic impedance of a continuously moving strip of material within predetermined limits or parameters.

v The novel features of the present invention, as well as additional objects and advantages thereof, will be understood more fully from the'following description when read in connection with the accompanying drawings, in which:

Figure 1 is a plan view of one form of apparatus cording to the present invention;

Figure 2 is a view in sectional elevation of the appara- 2,913,838 Patented Nov. 24, 1959 ice tus taken along the line 2,2 of Figure 1 and looking in the direction of the appended arrows;

I Figure 3 is a view in sectional elevation of a portion of the apparatus taken along the line 33 of Figure 1 and looking in the direction of the appended arrows; and

Figure 4 is a view in sectional elevation of the calender taken along the line 4--4 of Figure l and looking in the direction of the appended arrows. I

In the illustrative embodiment of the invention exemplified'in the drawing, in which similar characters designate similar parts throughout, a complete apparatus includes a supply spool assembly 11, a calender 31, an acoustic impedance measuring device 71, a take-up spool mechanism 91 and a driving mechanism 101. This apparatus has been designed to calender a strip of thermoplasticmaterial 12, such as nylon or Orlon for example.

A spool 13 of the material to be processed is mounted on a shaft 15 which is carried by hearing brackets 17 and 19. One of these brackets 19 has a longitudinal slot 21 extending downwardly from the bearing 23. A screw 25 which is set in the bracket transversely of the slot 21, is provided so that the arms of the bracket 19 I formed by the slot may be drawn together. Hence the pressure between the bearing portion 23 of the bracket 19 and the journal 27 of the shaft 15 may be varied to control the rotation of the shaft by means of friction.

The calender 31 is carried in a frame comprising essentially two side members 33 and a top member 35. A pair of bearings 37 and 39 are mounted in each of the side members 33. These bearings are mounted for sliding movement in a vertical direction and support, respectively, the calender rollers 41 and 43. Looking in the direction of the roller axes, the bearings 37 and 39 have a substantially U-shaped contour and the bearing surfaces thereof are semi-circular in contour. The lower bearings 37 will exert an upward pressure on the roller 41 while the upper bearings 39 exert a downward pressure on'the roller 43. A leaf spring 45 is supported across the top of the calender and one end thereof engages each of the upper bearings 39. The spring is held together at its center by a securing member 47 which also provides a bearing surface. A threaded stud 49 is secured in a tapped hole provided in the upper member 35 of the calender frame and is aligned so that its lower end will bear on the bearing surface provided on the securing member 47. A crank 51 is attached to the upper end of the screw 49.

The rollers 41 and 43 are hollow and are open at one end so that heating elements extend within the rollers. In order to mount such heating elements, a bracket 53 is mounted on one of the side members 33. A pair of hollow sleeve members 55 are rigidly attached at one end to the bracket 53 by means of nuts 56, for example, and have tapped holes 57 provided in their opposite ends. These tapped ends of the sleeves 55 extend into the cavities in the rollers 41 and 43. A ceramic coil holder 59,

for instance, is screwed into each of the tapped holes 57 and carries a heating coil 61 which will provide an even heat over the surfaces of the rollers. The coil 61 may be connected to a source of electrical energy, which is not shown, by means of lead wires 63.

A pair of meshing gears 65 and 67 are attached to extensions of the rollers 41 and 43 to provide a positive drive for the rollers.

Mounted at the front of the calender is a ladder type bracket 69 carrying parallel bars 70 which are mounted transversely of the path of travelof the strip 12. These bars 70 may be stationary or they may be in the form of rollers whose function is to smooth out the strip 12 as it passes between them, to provide a predetermined 3 amount of frictional drag and to provide an even tension across the strip.

The acoustic impedance measuring device 71 includes a hollow tube 73, and a means for providing a known acoustic signal in the tube which means include an oscillater 75, an amplifier 76 and a transducer 77. A small aperture 79 is provided in the tube and is aligned so that the strip of material 12 will pass over this aperture. A microphone 81 is mounted on a support member 82 over the tube 73 so that its diaphragm is adjacent the aperture 79. The support member 82 also carries a pair of parallel guide bars 83 positioned on either side ofthe tube 73. These bars 83 hold the strip 12 against the tube 73 as it passes over the aperture 79 therein. The microphone 81 may be connected to an instrument such as a calibrated detector 85 which will give instantaneous readings of the signal picked up by the microphone as the material passes over the tube 73. The acoustic impedance measuring device described herein by way of example is the subject matter of a copendin'g application, Serial No. 412,360, entitled An Acoustic Impedance Measuring Apparatus, filed on behalf of S. A. Caldwell and assigned to the assignee of the present application.

The take-up spool mechanism comprises a shaft 93 carried on bearing brackets 94 and 95 and carrying a take-up spool 97 fixed at one end thereof and a small belt pulley 99 fixed at the other end thereof.

A driving mechanism 101 comprises a motor 103 and a speed reduction mechanism 105. The speed reduction mechanism is connected to the lower roller 41 of the calender 31 by means of a shaft 107 and a coupling 109. A belt pulley 111 is mounted on a shaft 107. This pulley 111 is aligned with the pulley 99 of the take-up mechanism and is somewhat larger in diameter than the pulley 99 so that the rotational speed of the shaft 93 will be somewhat greater than the rotational speed of the shaft 107. This arrangement is required so that the take-up mechanism 91 will tend to draw the strip out of the calender rollers at a rate faster than the rate provided by the calender and hence provide a constant tension on the strip between these points. In order to provide this tension, a certain amount of slip will occur between the pulley 99 and a belt 113 which couples the pulleys 99 and 111. In order to provide the required tension in the belt 113, an arm 115 is pivotally secured at one end to the bearing bracket 95 of the take-up mechanism. An idler pulley 117 ismounted at the other end of the arm 115 and is positioned at a point which is intermediate the pulleys 99 and 111. The arm 115 is biased to keep a constant tension on the belt by means of a spring 119 which is secured to the arm 115 at a point intermediate its ends and to the base member 96.

Operation A spool of material may be securely fixed to the shaft by any known means. The strip from the spool is then fed through the parallel bars 70, between the calender rollers 41 and 43, through the measuring device 81, and is attached to the takeup spool 97 which is fixed to the shaft 93. The main drive for the strip is provided by the drive motor 103 through the calender rollers. The amount of drag on the strip may be varied by threading the strip through a greater or lesser number of bars or rollers 70 and also by adjusting the drag means provided on the bracket 19.

The heat applied by the rollers 41 and 43 and the speed at which these rollers are driven is variable to extend the range of acoustic impedances that might be obtained from the apparatus. However, it has been found that with a fixed roller speed and with a fixed heat applied uniformly across the surfaces of the rollers, a wide range of irnpedances can be produced by varying the pressure of the rollers only. The present apparatus, therefore, is designed so that the pressure applied to the rollers may be varied during the operation of the apparatus.

The impedance measuring device must be calibrated prior to the processing of a strip of material. The method for doing this is described in detail in the above mentioned copending application and it is believed that a detailed description is not necessary here. Very briefly, however, this is accomplished by placing a material having a known acoustic impedance in the device, passing the known acoustic signal through it and observing the upper and lower limits of acceptable response as indicated on the calibrated detector. Having established these limits, the acoustic impedance of the production strip being processed may be kept within the limits by varying the pressure on the calender rollers. Since variations in the acoustic impedance usually occur gradually over wide areas of material, uniformity may be controlled by making a correction on the calendar when the detector indicates that the impedance is changing in one direction or the other.

In order to obtain accurate and consistent measurements, it is desired that a certain and substantially constant tension be provided on the strip 12 as it emerges from the calender 31 and passes over the acoustic measuring device 71. Such tension is provided by the arrangement of the pulleys 99 and 111 and the means for keeping a tension on the belt 113 which couples these pulleys. The pulley 99 of the take-up mechanism is somewhat smaller than the pulley 111 of the drive mechanism. This means that the shaft 93 of the take-up mechanism will rotate at a faster rate than the shaft 107 of the drive mechanism. However, the linear rate of travel of the strip 12 is controlled by the calender rollers which are directly coupled to the shaft 107 so that the take-up mechanism, in attempting to drive the strip 12 at a faster rate, will create a tension on the strip.

To maintain this tension on the strip substantially constant, the belt 113 is permitted to slip on the pulley 99. The torque applied to the pulley 99 by the belt 113 is controlled by the tension applied to the belt 113, and this tension is, in turn, regulated by the idler pulley 117 and its biasing spring 119.

With this mechanism, one of the problems in transducer design, that of obtaining damping material with certain acoustic properties, has been greatly reduced. When the acoustic parameters for the damping material necessary to obtain the desired response of a transducer have been calculated or measured, the limits may be transferred to the detector of the acoustic impedance measuring device. Material can be calendered and the desired acoustic impedance limits can be maintained at the same time. The result is a damping material with a uniform, prescribed acoustic impedance.

What is claimed is:

1. Apparatus for processing a continuously moving 4 strip of a material to a uniform acoustic impedance comprising a calender having a pair of rollers, means for driving said rollers to drive said strip between said rollers at a fixed rate, means providing a continuous control for varying the pressure applied between said rollers, a takeup mechanism for said strip, means coupled to said roller driving means for frictionally driving said take-up mechanism, said take-up mechanism tending to draw said strip from said rollers at a rate faster than the rate provided by said rollers whereby a constant tension is provided on said strip, a mechanism for passing a known acoustic signal through said calendered and tensioned strip, and means for detecting said signal and indicating the impedance of said strip to the passage of said signal, said detected signal indicating the desired pressure variation to be applied to said rollers to provide a material having a uniform acoustic impedance.

2. Apparatus for processing a continuous strip of damping material to a uniform acoustic impedance while it is in motion, said apparatus comprising a calender having a pair of rollers for compressing said strip, means associated with said calender, for providing an even tension across the width of said strip as it enters said rollers, a mechanism for producing a known acoustic signal and directing said signal through said compressed strip, means for detecting said signal and indicating the resistance of said material to the passage of said signal, said resistance being determined by the amount of compression and the amount of tension on said strip, means for driving said strip between said calender rollers and over said signal directing mechanism, means associated with said driving means for maintaining a substantially constant tension on said strip as it passes over said signal directing mechanism and means associated with said calender to provide a continuous control for adjusting the pressure between said rollers, said detecting and indicating means determining the desired pressure adjustment for providing a uniform impedance along said strip.

3. Apparatus for processing a continuously moving strip of a damping material while it is in motion to a uniform acoustic impedance, said apparatus comprising, in combination, a calender having a pair of rollers for pressing said strip, means for driving said rollers at a constant rate, means associated with said calender for readily varying the pressure applied between said rollers, means for holding a supply reel of said material, means for maintaining a constant and even tension across said strip as it enters said rollers, said tension maintaining means comprising a drag mechanism on said supply reel and a rack mounted adjacent said rollers carrying a plurality of parallel bars mounted transversely of said strip and ahead of said rollers, means for producing a uniform heat across the surfaces of said rollers, a take-up mechanism for said strip, means coupled to said roller driving means tending to drive said strip take-up mechanism at a rate faster than the driving rate of said rollers, said lastnamed means maintaining said strip under a substantially constant tension as it leaves said rollers, a mechanism positioned between said calender and said take-up mechanism for passing a known acoustic signal through said pressed and tensioned strip, and means for indicating the relative impedance of said calendered strip to the passage of said acoustic signal, said indicated impedance determining the variation in pressure to be applied to said strip.

4. Apparatus for processing a strip of woven material to a uniform acoustic impedance comprising a calender having a pair of rollers for compressing said strip of material, means for readily varying the pressure between said rollers, means for driving said rollers whereby said strip is drawn through said rollers at a uniform rate, smoothing means comprising a rack positioned ahead of said rollers carrying a plurality of parallel members mounted transversely of the direction of movement of said strip to provide a tortuous path for said strip, means driven by said roller driving means for drawing said compressed strip from said calender, said strip drawing means tending to draw said strip at a rate faster than the rate provided by said roller driving means whereby a constant tension is maintained on said strip as it is drawn from said rollers, means for passing a known acoustic signal through said compressed and tensioned strip, means for translating said acoustic signal into an electrical signal, and means for measuring said electrical signal to provide a continuous reading of the acoustic impedance of said strip material whereby the desired pressure variation to be applied to said rollers is indicated.

5. Apparatus for processing a strip of damping material to a uniform acoustic impedance comprising, in combination, a calender having a pair of pressure rollers, means for readily varying the pressure between said rollers whereby the acoustic impedance of said material is controlled, means for driving said rollers at a constant rate, means enclosed within said rollers for producing a uniform heat along the surfaces of said rollers, means associated with said calender for maintaining a uniform tension across said strip as it enters said rollers, a take'up mechanism for said strip comprising a take-up spool and a drive pulley, a friction belt coupling said drive pulley and said roller driving means, means associated with said take-up mechanism for adjusting the tension on said belt, said take-up mechanism tending to draw said strip from said rollers at a rate faster than the rate provided by said rollers whereby a constant tension is maintained on said strip as it leaves said rollers, means for passing a known acoustic signal through said calendered and tensioned strip, means for translating said acoustic signal into an electrical signal, and means for measuring said electrical signal to determine the'relative acoustic impedance of said strip of material to the passage of said known signal whereby the pressure to be applied between said rollers is indicated.

References Cited in the file of this patent UNITED STATES PATENTS 160,594 Hebdon Mar. 9, 1875 1,261,225 Galloway Apr. 2, 1918 2,232,966 Peterson Feb. 25, 1941 2,457,695 Liskow Dec. 28, 1948 2,549,038 Zenner Apr. 17, 1951 

